Power transfer coil

ABSTRACT

The present invention suppresses leakage magnetic field. A power transfer coil configured to transmit or receive power includes: an inner coil; a first outer coil formed so as to surround the inner coil such that a magnetic flux opposite in phase to a magnetic flux outside the inner coil is generated outside the first outer coil, the first outer coil having one end connected to a first terminal and the other end connected to one end of the inner coil; and a second outer coil formed so as to surround the inner coil such that a magnetic flux opposite in phase to the magnetic flux outside the inner coil is generated outside the second outer coil, the second outer coil having one end connected to a second terminal and the other end connected to the other end of the inner coil.

TECHNICAL FIELD

The present invention relates to a power transfer coil. The presentinvention claims priority from Japanese Patent Application No.2016-95947 filed on May 12, 2016, the contents of which are incorporatedherein by reference for the designated states where incorporation byreference of documents is allowed.

BACKGROUND ART

Patent Document 1 discloses a coil antenna comprising a main coil formedby winding a conductor wire about a reference axis, and an auxiliarycoil arranged so as to be spaced apart from the main coil at apredetermined interval as well as being electrically connected in seriesto the main coil such that the same alternating current as that flowingin the main coil is flowed therein.

RELATED ART DOCUMENTS Patent Documents

Patent Document 1: Japanese Unexamined Patent Application PublicationNo. 2015-15852

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

When transmitting power by using inductive coupling, leakage magneticfield occurs from a power transmitting coil or a power receiving coil.Leakage magnetic field is likely to cause interference on otherelectronic devices and may also affect the human body.

Patent Document 1 discloses a configuration in which an auxiliary coilis arranged so as to be spaced apart from a main coil at a predeterminedinterval in a direction of a reference axis, so that leakage magneticfield is suppressed.

Accordingly, an object of the present invention is to provide atechnique in which leakage magnetic field is suppressed.

Means for Solving the Problems

The present application includes several means for solving at least aportion of the problems described above, and examples thereof are asfollows. In order to solve the problems described above, a powertransfer coil according to the present invention comprises: an innercoil; a first outer coil formed so as to surround the inner coil suchthat a magnetic flux opposite in phase to a magnetic flux outside theinner coil is generated outside the first outer coil, the first outercoil having one end connected to a first terminal and the other endconnected to one end of the inner coil; and a second outer coil formedso as to surround the inner coil such that a magnetic flux opposite inphase to the magnetic flux outside the inner coil is generated outsidethe second outer coil, the second outer coil having one end connected toa second terminal and the other end connected to the other end of theinner coil.

Effects of the Invention

According to the present invention, leakage magnetic field can besuppressed. Problems, configurations and effects other than thosedescribed above will be made clear by descriptions of the embodimentsdescribed below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing showing an example of a wireless power transfersystem according to a first embodiment;

FIG. 2 is a drawing showing a configuration example of a power transfercoil;

FIG. 3 is a drawing showing an equivalent circuit of the power transfercoil;

FIG. 4 is a drawing describing a relation between the sizes of an innercoil and outer coils and a relation between the numbers of turns of theinner coil and outer coils;

FIG. 5 is a drawing describing a magnetic field generated by the powertransfer coil;

FIG. 6 is a drawing showing an example of another power transfer coil;

FIG. 7 is a drawing describing a power receiving process of the powertransfer coil of FIG. 6;

FIG. 8 is a drawing showing a configuration example of a power transfercoil according to a second embodiment;

FIG. 9 is a drawing showing an equivalent circuit of the power transfercoil;

FIG. 10 is a drawing describing a magnetic field generated by the powertransfer coil;

FIG. 11 is a drawing showing a configuration example of a power transfercoil according to a third embodiment;

FIG. 12 is a drawing showing an equivalent circuit of the power transfercoil;

FIG. 13 is a drawing describing a magnetic field generated by the powertransfer coil;

FIG. 14 is a drawing describing power transmission efficiency;

FIG. 15 is a graph showing a relation between a distance from a powertransfer coil and a magnitude of leakage magnetic field;

FIG. 16 is a graph showing a relation between misalignment of the powertransfer coils and transmission properties;

FIG. 17 is a drawing showing a configuration example of a power transfercoil according to a fourth embodiment;

FIG. 18 is a drawing showing an equivalent circuit of the power transfercoil;

FIG. 19 is a drawing describing a magnetic field generated by the powertransfer coil;

FIG. 20 is a drawing showing a block configuration example of a powersupplying device and power receiving device according to a fifthembodiment;

FIG. 21 is a flowchart showing an operation example of a controller ofthe power supplying device;

FIG. 22 is a drawing showing a first application example of the powersupplying device and power receiving device;

FIG. 23 is a drawing showing a second application example of the powersupplying device and power receiving device;

FIG. 24 is a drawing showing a third application example of the powersupplying device and power receiving device;

FIG. 25 is a drawing showing a fourth application example of the powersupplying device and power receiving device; and

FIG. 26 is a drawing showing a fifth application example of the powersupplying device and power receiving device.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to the drawings.

Connecting to a connector to charge a portable device such as a mobiledevice has become more troublesome as the devices have become smallerand thinner, and thus, there is a growing demand to perform charging bywireless power transfer. In addition, using a wire to charge an electricvehicle while raining or the like would allow water to enter theconnector and cause possible deterioration of its junction, and thus, itis preferable to perform charging by wireless power transfer. Further, acare receiver or the like would have difficulties in connecting a wireto a connector to charge a device such as a stair elevator or a movablelift for nursing care use, and thus, it is preferable to performcharging by wireless power transfer.

Studies are being conducted on wireless power transfer using radio wavessuch as microwaves and wireless power transfer using inductive coupling(electromagnetic induction). Wireless power transfer using microwavesprovides excellent transmission distance but is poor in transmissionefficiency, making it hardly suitable for practical use. In contrast,wireless power transfer using inductive coupling provides a transmissiondistance of a few to ten-odd centimeters but can achieve a hightransmission efficiency of approximately 90% for the coils used intransmitting and receiving power. For this reason, it is considered thattransmitting power using inductive coupling would become the mainstreamfor wireless power transfer.

Power transmitting frequencies used for inductive coupling include bandsof 100 kHz, 400 kHz, 6.78 MHz, 13.56 MHz and the like. Wireless powertransfer using inductive coupling provides a transmission distance thatis relatively short but allows leakage magnetic field to occur from thepower transmitting coil or the power receiving coil. When consideringadverse effects on other electronic devices and on the human body, it isnecessary to suppress this leakage magnetic field as low as possible.

First Embodiment

FIG. 1 is a drawing showing an example of a wireless power transfersystem 1 according to a first embodiment. As shown in FIG. 1, thewireless power transfer system 1 includes a charger 2 and a mobiledevice 3.

The mobile device 3 to be charged with power is placed above the charger2. The charger 2 has a built-in power transfer coil 10 a configured totransmit power to the mobile device 3.

The mobile device 3 is a smartphone, a tablet computer, a mobile phoneor the like. The mobile device 3 has a built-in power transfer coil 10 bconfigured to receive the power from the charger 2.

The power transfer coils 10 a and 10 b have the same shape andconfiguration. Therefore, when there is no need to distinguish betweenthe power transfer coils 10 a and 10 b, the coils will be collectivelyreferred to as power transfer coil 10 hereinafter. Note that there arecases where the power transfer coils 10 a and 10 b have different shapesand configurations as described below.

FIG. 2 is a drawing showing a configuration example of the powertransfer coil 10. As shown in FIG. 2, the power transfer coil 10includes terminals T11 and T12, an inner coil 11, outer coils 12 a and12 b, and capacitor elements 13 a and 13 b. The inner coil 11 and theouter coils 12 a and 12 b are formed on the same planar surface(including substantially same planar surface; the same applies to theterm hereinafter). Note that, although FIG. 2 shows the inner coil 11and the outer coils 12 a and 12 b each wound so as to have gapstherebetween, the coils are actually wound more tightly. The sameapplies to the coils described below.

The outer coils 12 a and 12 b have the same shape (includingsubstantially same shape; the same applies to the term hereinafter) andare arranged at the same position. The outer coils 12 a and 12 b have acircular shape with its radius denoted as “r12”.

The inner coil 11 has a circular shape with its radius denoted as “r11”which is smaller than the radius “r12” of the outer coils 12 a and 12 b(r11<r12). The inner coil 11 is formed inside a loop of the outer coils12 a and 12 b.

The inner coil 11 is connected between the outer coils 12 a and 12 b viathe capacitor elements 13 a and 13 b. A combined capacitance of thecapacitor elements 13 a and 13 b is a value that resonates with acombined self-inductance of the inner coil 11 and outer coils 12 a and12 b at a power transmitting frequency.

The outer coil 12 a is formed so as to surround the inner coil 11. Theouter coil 12 a is formed such that a magnetic flux opposite in phase toa magnetic flux outside the inner coil 11 is generated outside the outercoil 12 a.

For example, the outer coil 12 a is formed such that a current is flowedin a direction opposite to a current flowing in the inner coil 11. Morespecifically, in a case where the current is flowing in the inner coil11 in a clockwise direction, the outer coil 12 a is formed such that thecurrent is flowed in a counterclockwise direction.

The outer coil 12 b is formed so as to surround the inner coil 11. Theouter coil 12 b is formed such that a magnetic flux opposite in phase tothe magnetic flux outside the inner coil 11 is generated outside theouter coil 12 b.

For example, the outer coil 12 b is formed such that a current is flowedin a direction opposite to the current flowing in the inner coil 11.More specifically, in a case where the current is flowing in the innercoil 11 in the clockwise direction, the outer coil 12 b is formed suchthat a current is flowed in the counterclockwise direction.

The outer coil 12 a has one end connected to the terminal T11 and theother end connected to the capacitor element 13 a. The outer coil 12 bhas one end connected to the terminal T12 and the other end connected tothe capacitor element 13 b. A current for generating a magnetic field inthe inner coil 11 and outer coils 12 a and 12 b is fed to the terminalsT11 and T12.

The power transfer coil 10 is formed so as to be symmetrical (linearlysymmetrical) when viewed from one end of the outer coil 12 a connectedto the terminal T11 and one end of the outer coil 12 b connected to theterminal T12.

FIG. 3 is a drawing showing an equivalent circuit of the power transfercoil 10. FIG. 3 shows the terminals T11 and T12 of FIG. 2.

An inductor L11 of FIG. 3 corresponds to the outer coil 12 a of FIG. 2.A capacitor element C11 of FIG. 3 corresponds to the capacitor element13 b of FIG. 2. An inductor L12 of FIG. 3 corresponds to the inner coil11 of FIG. 2. A capacitor element C12 of FIG. 3 corresponds to thecapacitor element 13 a of FIG. 2. An inductor L13 of FIG. 3 correspondsto the outer coil 12 b of FIG. 2.

As shown in FIG. 3, the equivalent circuit of the power transfer coil 10is also formed so as to be symmetrical (arrangement of elements arelinearly symmetrical) when viewed from one end of the outer coil 12 aconnected to the terminal T11 and one end of the outer coil 12 bconnected to the terminal T12.

Here, a relation between sizes of the inner coil 11 and outer coils 12 aand 12 b and a relation between the numbers of turns of the inner coil11 and outer coils 12 a and 12 b will be described.

FIG. 4 is a drawing describing the relation between the sizes of theinner coil 11 and outer coils 12 a and 12 b and the relation between thenumbers of turns of the inner coil 11 and outer coils 12 a and 12 b.

FIG. 4 shows current loops A1, A2 and A3. Radii of the current loops A1,A2 and A3 are respectively denoted as “a1”, “a2” and “a3”. In thisexample, a high frequency current I is flowing in the current loops A1and A2 in the clockwise direction, and a high frequency current I isflowing in the current loop A3 in a direction opposite (counterclockwisedirection) to the current loops A1 and A2.

Magnitude of the magnetic field generated by the current loop A1 isproportional to an area of the current loop A1 and the current flowingin the current loop A1. In other words, the magnitude of the magneticfield generated by the current loop A1 is proportional to “a1 ²×I”.

Thus, a condition to cancel leakage magnetic field in a far field of thecurrent loops A1, A2 and A3 is obtained by the following equation (1),considering the direction of the current:

based on (a1² +a2² −a3²)I=0,

a1² +a2² −a3²=0  (1)

In a case where the radii of the inner and middle current loops A1 andA2 are equal to each other, the condition to cancel leakage magneticfield in the far field of the current loops A1, A2 and A3 is obtained bythe following equation (2), where “a1=a2” is satisfied in equation (1):

based on 2a1²=a3²,

a3=2^(1/2) ×a1  (2)

From the above, leakage magnetic field can be cancelled in the far fieldby flowing a doubled high frequency current I in the current loop A1having the radius “a1” and by flowing a high frequency current I in thecurrent loop A3 having the radius “2^(1/2)×a1” in the oppositedirection.

Note that the region farther than λ/(2π) from a magnetic field source isreferred to as the far field, and the region closer than this isreferred to as a near field. “λ” denotes a wavelength of the power to bewirelessly transferred. For example, in a case where the powertransmitting frequency is 10 MHz, a boundary between the far field andthe near field is 4.8 m.

By applying the above-described conditions to the power transfer coil 10of FIG. 2, leakage magnetic field in the far field of the power transfercoil 10 can be suppressed. For example, the radius “r12” of the outercoils 12 a and 12 b of FIG. 2 is set to be 2^(1/2) times (includingapproximately 2^(1/2) times; the same applies to the term hereinafter)as large as the radius “r11” of the inner coil 11. In addition, thecoils are wound such that the current flowing in the inner coil 11 istwice as large as the current flowing in the outer coils 12 a and 12 b.For example, the coils are wound such that the number of turns of theinner coil 11 is twice (including approximately twice; the same appliesto the term hereinafter) as large as the sum of the number of turns ofthe outer coil 12 a and the number of turns of the outer coil 12 b.Thus, leakage magnetic field in the far field of the power transfer coil10 is suppressed.

Effects caused by leakage magnetic field that occurs at the time ofwireless power transfer is regarded critical in a case where otherelectronic devices and the like are placed at a relatively shortdistance of tens of centimeters to a few meters from the power transfercoil 10. For this reason, it is also important to suppress leakagemagnetic field in the near field.

Since the distance from the coil is short in the near field, it isconsidered that the shape of the coil and the like would affect leakagemagnetic field as well. By providing the configuration of the powertransfer coil 10 shown in FIG. 2, leakage power in the near field canalso be suppressed. In particular, the power transfer coil 10 is formedso as to be symmetrical when viewed from one end of each of the outercoils 12 a and 12 b respectively connected to the terminals T11 and T12,so that an effect of suppressing leakage magnetic field in the nearfield is enhanced. In addition, the equivalent circuit of the powertransfer coil 10 is also formed so as to be symmetrical, so that theeffect of suppressing leakage magnetic field in the near field isfurther enhanced.

FIG. 5 is a drawing describing the magnetic field generated by the powertransfer coil 10. FIG. 5 shows the power transfer coil 10 of FIG. 2 in asimplified manner. In FIG. 5, components that are the same as thoseshown in FIG. 2 are denoted by the same reference signs.

As shown in FIG. 5, in a case where current I is fed from the terminalT12, a magnetic flux generated by the inner coil 11 and a magnetic fluxgenerated by the outer coils 12 a and 12 b cause a magnetic flux as in amagnetic flux B11 shown in FIG. 5 extending from the front side of thedrawing plane toward the back side of the drawing plane to be generatedinside the inner coil 11.

Further, the magnetic flux generated by the inner coil 11 and themagnetic flux generated by the outer coils 12 a and 12 b cause amagnetic flux as in magnetic fluxes B12 a and B12 b shown in FIG. 5extending from the back side of the drawing plane toward the front sideof the drawing plane to be generated between the inner coil 11 and theouter coils 12 a and 12 b.

The magnetic flux generated by the inner coil 11 and the magnetic fluxgenerated by the outer coils 12 a and 12 b cause the magnetic fluxoutside the outer coils 12 a and 12 b to be “0” (including approximately0; the same applies to the term hereinafter). Namely, the power transfercoil 10 suppresses leakage magnetic field in its near field as well.Measurement results regarding a magnitude of leakage magnetic field withrespect to distance from the power transfer coil 10 will be describedbelow (FIG. 15).

In wireless power transfer using inductive coupling, coupling betweenthe power transfer coils at a power supplying end and power receivingend increases as the numbers of turns of the power transfer coilsincrease, so that power transmission efficiency is enhanced. However, anincrease in the numbers of turns of the power transfer coils causes anincrease in parasitic capacitance between the coils which further leadsto a decrease in a self-resonant frequency determined by this parasiticcapacitance and self-inductance of the power transfer coils. For thisreason, a frequency range that can be used for the power transmittingfrequency is decreased by the decreased amount of the self-resonantfrequency. In addition, a decrease in self-resonant frequency causes a Qfactor (sharpness) of the coil to deteriorate.

However, the power transfer coil 10 is provided with the capacitorelements 13 a and 13 b connected between the inner coil 11 and the outercoils 12 a and 12 b. By providing the capacitor elements 13 a and 13 b,an electric charge that accumulates between the turns of the coils whichcause parasitic capacitance of the power transfer coil 10 is accumulatedin the capacitor elements 13 a and 13 b, so that parasitic capacitanceis less likely to occur between the coils. Thus, in the power transfercoil 10, a decrease in the self-resonant frequency can be suppressed, sothat the numbers of turns of the inner coil 11 and outer coils 12 a and12 b can be increased. In other words, the power transfer coil 10 allowscoupling between the coils to be increased, so that transmissionefficiency is enhanced.

Further, for wireless power transfer using inductive coupling, when theshapes of the power transfer coils at the power supplying end and powerreceiving end are the same, coupling between the power transfer coils isincreased, so that transmission efficiency is enhanced. However, theremay be a case where the shapes of the power transfer coils at the powersupplying end and power receiving end differ from each other. Forexample, there may be a case where the charger 2 shown in FIG. 1 hasvarious mobile devices 3 placed thereon, the mobile devices 3 eachhaving a power transfer coil of different shape.

FIG. 6 is a drawing showing an example of another power transfer coil P.The power transfer coil P shown in FIG. 6 is a circular coil simplywound in one direction. The power transfer coil P configured to receivethe power is an example of a coil at a power receiving end.

FIG. 7 is a drawing describing a power receiving process of the powertransfer coil P of FIG. 6. FIG. 7 shows the power transfer coil 10 ofFIG. 5 in a simplified manner. In addition, FIG. 7 shows the powertransfer coil P (power transfer coils Pa and Pb of different size) ofFIG. 6 in a simplified manner.

In FIG. 7, the power transfer coil 10 configured to transmit power is apower transfer coil at the power supplying end (charger 2), and thepower transfer coils Pa and Pb configured to receive the power are powertransfer coils at the power receiving end (mobile device 3).Hereinafter, when there is no need to distinguish between the powertransfer coils Pa and Pb, the coils will be collectively referred to asthe power transfer coil P.

It is preferable that the inner coil 11 of the power transfer coil 10 atthe power supplying end is larger than the power transfer coil P at thepower receiving end. For example, in a case where the inner coil 11 issmaller than the power transfer coil Pa denoted by a dot-and-dash lineat the power receiving end, the magnetic flux B11 and the magneticfluxes B12 a and B12 b opposite in phase to the magnetic flux B11 enterthe power transfer coil Pa denoted by a dot-and-dash line. This allows adecrease in the power transmission efficiency of the power transfer coilPa denoted by the dot-and-dash line at the power receiving end.

On the other hand, in a case where the inner coil 11 is larger than thepower transfer coil Pb denoted by a dotted line at the power receivingend, only the unidirectional magnetic flux B11 enters the power transfercoil Pb denoted by the dotted line as long as the power transfer coil Pbis arranged inside the inner coil 11. Namely, the magnetic fluxes B12 aand B12 b opposite in phase to the magnetic flux B11 do not enter thepower transfer coil Pb denoted by the dotted line. This allows the powertransfer coil Pb denoted by the dotted line to suppress a decrease inpower transmission efficiency by the power transfer coil Pa denoted bythe dot-and-dash line.

In this manner, it is possible to provide a configuration in which thepower transfer coil at the power supplying end is the power transfercoil 10 and the power transfer coil at the power receiving end is thepower transfer coil P that differs from the power transfer coil 10. Inthis case, the inner coil 11 of the power transfer coil 10 is set to belarger than the power transfer coil P in order to suppress a decrease inpower transmission efficiency.

Nevertheless, optimum power transmission efficiency can be achieved whenthe power transfer coil at the power receiving end is identical to thepower transfer coil 10 at the power supplying end (that is, when thepower transfer coil at the power receiving end is another power transfercoil 10). For example, the magnetic flux B11 shown in FIG. 7 is receivedby the inner coil 11 of the power transfer coil 10 at the powerreceiving end, and the magnetic fluxes B12 a and B12 b are received by aloop (space) between the inner coil 11 and the outer coils 12 a and 12 bof the power transfer coil 10 at the power receiving end, so thatoptimum power transmission efficiency can be achieved.

As described above, the power transfer coil 10 includes: the outer coil12 a formed so as to surround the inner coil 11 such that a magneticflux opposite in phase to the magnetic flux outside the inner coil 11 isgenerated outside the outer coil 12 a, the outer coil 12 a having oneend connected to the terminal T11 and the other end connected to one endof the inner coil 11; and the outer coil 12 b formed so as to surroundthe inner coil 11 such that a magnetic flux opposite in phase to themagnetic flux outside the inner coil 11 is generated outside the outercoil 12 b, the outer coil 12 b having one end connected to the terminalT12 and the other end connected to the other end of the inner coil 11.Thus, the power transfer coil 10 can suppress leakage magnetic field inthe far field and near field.

In addition, the inner coil 11 and the outer coils 12 a and 12 b of thepower transfer coil 10 are each formed so as to be symmetrical whenviewed from one end of the outer coil 12 a and one end of the outer coil12 b. Further, the equivalent circuit of the power transfer coil 10 isalso formed so as to be symmetrical when viewed from one end of theouter coil 12 a and one end of the outer coil 12 b. Thus, the powertransfer coil 10 can suppress leakage magnetic field in the near field.

In addition, a current approximately twice as large as the sum of thecurrent flowing in the outer coil 12 a and the current flowing in theouter coil 12 b is flowed in the inner coil 11 of the power transfercoil 10. Further, the radius of the outer coils 12 a and 12 b isapproximately 2^(1/2) times as large as the radius of the inner coil 11.Thus, the power transfer coil 10 can suppress leakage magnetic field inthe near field.

In addition, the power transfer coil 10 includes the capacitor element13 a connected between the inner coil 11 and the outer coil 12 a, andthe capacitor element 13 b connected between the inner coil 11 and theouter coil 12 b. Thus, the power transfer coil 10 can suppress adecrease in the self-resonant frequency.

In addition, the power transfer coil 10 has the inner coil 11 and outercoils 12 a and 12 b formed on the same planar surface, so thatminiaturization can be achieved.

Second Embodiment

In the first embodiment, the inner coil 11 is connected between twoouter coils 12 a and 12 b. In a second embodiment, the outer coil isconnected between two inner coils.

FIG. 8 is a drawing showing a configuration example of a power transfercoil 20 according to the second embodiment. As shown in FIG. 8, thepower transfer coil 20 includes terminals T21 and T22, inner coils 21 aand 21 b, an outer coil 22, and capacitor elements 23 a and 23 b. Theinner coils 21 a and 21 b and the outer coil 22 are formed on the sameplanar surface. The power transfer coil 20 is applied to a powersupplying device (such as the charger 2 of FIG. 1) configured totransmit power or a power receiving device (such as the mobile device 3of FIG. 1) configured to receive the power.

The inner coils 21 a and 21 b have the same shape and are arranged atthe same position. The inner coils 21 a and 21 b have a circular shapewith its radius denoted as “r21”.

The inner coil 21 a has one end connected to the terminal T21 and theother end connected to the capacitor element 23 b. The inner coil 21 bhas one end connected to the terminal T22 and the other end connected tothe capacitor element 23 a. A current for generating a magnetic field inthe inner coils 21 a and 21 b and outer coil 22 is fed to the terminalsT21 and T22.

The outer coil 22 has a circular shape with its radius denoted as “r22”which is larger than the radius “r21” of the inner coils 21 a and 21 b(r22>r21). The inner coils 21 a and 21 b are formed inside a loop of theouter coil 22.

The outer coil 22 is formed so as to surround the inner coils 21 a and21 b. The outer coil 22 is formed such that a magnetic flux opposite inphase to a magnetic flux outside the inner coils 21 a and 21 b isgenerated outside the outer coil 22.

For example, the outer coil 22 is formed such that a current is flowedin a direction opposite to a current flowing in the inner coils 21 a and21 b. More specifically, in a case where the current is flowing in theinner coils 21 a and 21 b in the clockwise direction, the outer coil 22is formed such that the current is flowed in the counterclockwisedirection.

The outer coil 22 is connected between the inner coils 21 a and 21 b viathe capacitor elements 23 a and 23 b. A combined capacitance of thecapacitor elements 23 a and 23 b is a value that resonates with acombined self-inductance of the inner coils 21 a and 21 b and outer coil22 at the power transmitting frequency.

The power transfer coil 20 is formed so as to be symmetrical when viewedfrom one end of the inner coil 21 a connected to the terminal T21 andone end of the inner coil 21 b connected to the terminal T22.

FIG. 9 is a drawing showing an equivalent circuit of the power transfercoil 20. FIG. 9 shows the terminals T21 and T22 of FIG. 8.

An inductor L21 of FIG. 9 corresponds to the inner coil 21 a of FIG. 8.A capacitor element C21 of FIG. 9 corresponds to the capacitor element23 b of FIG. 8. An inductor L22 of FIG. 9 corresponds to the outer coil22 of FIG. 8. A capacitor element C22 of FIG. 9 corresponds to thecapacitor element 23 a of FIG. 8. An inductor L23 of FIG. 9 correspondsto the inner coil 21 b of FIG. 8.

As shown in FIG. 9, the equivalent circuit of the power transfer coil 20is also formed so as to be symmetrical when viewed from one end of theinner coil 21 a connected to the terminal T21 and one end of the innercoil 21 b connected to the terminal T22.

The relation between the sizes of the inner coils 21 a and 21 b andouter coil 22 and the relation between the numbers of turns of the innercoils 21 a and 21 b and outer coil 22 are the same as those of the firstembodiment. For example, the radius “r22” of the outer coil 22 shown inFIG. 8 is set to be 2^(1/2) times as large as the radius “r21” of theinner coils 21 a and 21 b. In addition, the coils are wound such thatthe current flowing in the inner coils 21 a and 21 b is twice as largeas the current flowing in the outer coil 22. For example, the coils arewound such that the sum of the number of turns of the inner coil 21 aand the number of turns of the inner coil 21 b is twice as large as thenumber of turns of the outer coil 22. Thus, leakage magnetic field inthe far field of the power transfer coil 20 is suppressed.

By providing the configuration of the power transfer coil 20 shown inFIG. 8, leakage power in the near field can also be suppressed. Inparticular, the power transfer coil 20 is formed so as to be symmetricalwhen viewed from one end of the inner coil 21 a connected to theterminal T21 and one end of the inner coil 21 b connected to theterminal T22, so that the effect of suppressing leakage magnetic fieldin the near field is enhanced. In addition, the equivalent circuit ofthe power transfer coil 20 is also formed so as to be symmetrical, sothat the effect of suppressing leakage magnetic field in the near fieldis further enhanced.

FIG. 10 is a drawing describing the magnetic field generated by thepower transfer coil 20. FIG. 10 shows the power transfer coil 20 of FIG.8 in a simplified manner. In FIG. 10, components that are the same asthose shown in FIG. 8 are denoted by the same reference signs.

As shown in FIG. 10, in a case where current I is fed from the terminalT22, a magnetic flux generated by the inner coils 21 a and 21 b and amagnetic flux generated by the outer coil 22 cause a magnetic flux as ina magnetic flux B21 shown in FIG. 10 extending from the back side of thedrawing plane toward the front side of the drawing plane to be generatedinside the inner coils 21 a and 21 b.

Further, the magnetic flux generated by the inner coils 21 a and 21 band the magnetic flux generated by the outer coil 22 cause a magneticflux as in magnetic fluxes B22 a and B22 b shown in FIG. 10 extendingfrom the front side of the drawing plane toward the back side of thedrawing plane to be generated between the inner coils 21 a and 21 b andthe outer coil 22.

The magnetic flux generated by the inner coils 21 a and 21 b and themagnetic flux generated by the outer coil 22 cause the magnetic fluxoutside the outer coil 22 to be “0”. Namely, the power transfer coil 20suppresses leakage magnetic field in its near field as well.

Power transmission efficiency based on the numbers of turns of the powertransfer coil at the power supplying end and power transfer coil at thepower receiving end is the same as that of the first embodiment, anddescriptions thereof will be omitted as appropriate. In addition, powertransmission efficiency based on the shapes of the power transfer coilat the power supplying end and power transfer coil at the powerreceiving end is also the same as that of the first embodiment, anddescriptions thereof will be omitted as appropriate.

As described above, the power transfer coil 20 includes the outer coil22 formed so as to surround the inner coils 21 a and 21 b such that amagnetic flux opposite in phase to the magnetic flux outside the innercoils 21 a and 21 b is generated outside the outer coil 22, the outercoil 22 having one end connected to the inner coil 21 a and the otherend connected to the inner coil 21 b. Thus, the power transfer coil 20can suppress leakage magnetic field in the far field and near field.

In addition, the inner coils 21 a and 21 b and the outer coil 22 of thepower transfer coil 20 are each formed so as to be symmetrical whenviewed from one end of the inner coil 21 a and one end of the inner coil21 b. Further, the equivalent circuit of the power transfer coil 20 isalso formed so as to be symmetrical when viewed from one end of theinner coil 21 a and one end of the inner coil 21 b. Thus, the powertransfer coil 20 can suppress leakage magnetic field in the near field.

In addition, a current approximately twice as large as the currentflowing in the outer coil 22 is flowed in the inner coils 21 a and 21 bof the power transfer coil 20. Further, the radius of the outer coil 22is approximately 2^(1/2) times as large as the radius of the inner coils21 a and 21 b. Thus, the power transfer coil 20 can suppress leakagemagnetic field in the near field.

In addition, the power transfer coil 20 includes the capacitor element23 b connected between the inner coil 21 a and the outer coil 22, andthe capacitor element 23 a connected between the inner coil 21 b and theouter coil 22. Thus, the power transfer coil 20 can suppress a decreasein the self-resonant frequency.

In addition, the power transfer coil 20 has the inner coils 21 a and 21b and outer coil 22 formed on the same planar surface, so thatminiaturization can be achieved.

Third Embodiment

In the first embodiment, two outer coils 12 a and 12 b surrounding theinner coil 11 have the same shape and are arranged in the same position.In a third embodiment, two outer coils surrounding the inner coil arearranged at separate positions.

FIG. 11 is a drawing showing a configuration example of a power transfercoil 30 according to the third embodiment. As shown in FIG. 11, thepower transfer coil 30 includes terminals T31 and T32, an inner coil 31,outer coils 32 a and 32 b, and capacitor elements 33 a and 33 b. Theinner coil 31 and the outer coils 32 a and 32 b are formed on the sameplanar surface. The power transfer coil 30 is applied to a powersupplying device (such as the charger 2 of FIG. 1) configured totransmit power or a power receiving device (such as the mobile device 3of FIG. 1) configured to receive the power.

The outer coils 32 a and 32 b have the same shape and are arranged atseparate positions. The outer coils 32 a and 32 b each have a crescentshape extending along the circular shape of the inner coil 31 andcollectively form a circular shape. The outer coil 32 a surrounds half(including substantially half; the same applies to the term hereinafter)of the inner coil 31, and the outer coil 32 b surrounds the remaininghalf of the inner coil 31.

The inner coil 31 is connected between the outer coils 32 a and 32 b viathe capacitor elements 33 a and 33 b. A combined capacitance of thecapacitor elements 33 a and 33 b is a value that resonates with acombined self-inductance of the inner coil 31 and outer coils 32 a and32 b at the power transmitting frequency.

The inner coil 31 has a circular shape. The inner coil 31 is arranged soas to be surrounded by the outer coils 32 a and 32 b outside a loop ofeach of the outer coils 32 a and 32 b.

The outer coil 32 a forms a loop outside the inner coil 31 and is formedsuch that a magnetic flux opposite in phase to a magnetic flux outsidethe inner coil 31 is generated outside this loop. For example, the outercoil 32 a is formed such that a current is flowed in a directionopposite to a current flowing in the inner coil 31. More specifically,in a case where the current is flowing in the inner coil 31 in thecounterclockwise direction, the outer coil 32 a is formed such that thecurrent is flowed in the clockwise direction.

The outer coil 32 b forms a loop outside the inner coil 31 and is formedsuch that a magnetic flux opposite in phase to the magnetic flux outsidethe inner coil 31 is generated outside this loop. For example, the outercoil 32 b is formed such that a current is flowed in a directionopposite to the current flowing in the inner coil 31. More specifically,in a case where the current is flowing in the inner coil 31 in thecounterclockwise direction, the outer coil 32 b is formed such that thecurrent is flowed in the clockwise direction.

The outer coil 32 a has one end connected to the terminal T31 and theother end connected to the capacitor element 33 a. The outer coil 32 bhas one end connected to the terminal T32 and the other end connected tothe capacitor element 33 b. A current for generating a magnetic field inthe inner coil 31 and outer coils 32 a and 32 b is fed to the terminalsT31 and T32.

The power transfer coil 30 is formed so as to be symmetrical when viewedfrom one end of the outer coil 32 a connected to the terminal T31 andone end of the outer coil 32 b connected to the terminal T32.

FIG. 12 is a drawing showing an equivalent circuit of the power transfercoil 30. FIG. 12 shows the terminals T31 and T32 of FIG. 11.

An inductor L31 of FIG. 12 corresponds to the outer coil 32 a of FIG.11. A capacitor element C31 of FIG. 12 corresponds to the capacitorelement 33 a of FIG. 11. An inductor L32 of FIG. 12 corresponds to theinner coil 31 of FIG. 11. A capacitor element C32 of FIG. 12 correspondsto the capacitor element 33 b of FIG. 11. An inductor L33 of FIG. 12corresponds to the outer coil 32 b of FIG. 11.

As shown in FIG. 12, the equivalent circuit of the power transfer coil30 is also formed so as to be symmetrical when viewed from one end ofthe outer coil 32 a connected to the terminal T31 and one end of theouter coil 32 b connected to the terminal T32.

The relation between the sizes of the inner coil 31 and outer coils 32 aand 32 b and the relation between the numbers of turns of the inner coil31 and outer coils 32 a and 32 b are obtained from the equations (1) and(2). For example, an area of the inner coil 31 is set to be equal to thesum of the areas of the outer coils 32 a and 32 b. In addition, theinner coil 31 and the outer coils 32 a and 32 b are wound such that thecurrent flowing in the coils are the same as each other. For example,the coils are wound such that the numbers of turns of the inner coil 31and outer coils 32 a and 32 b are equal to one another. Thus, leakagemagnetic field in the far field of the power transfer coil 30 issuppressed.

By providing the configuration of the power transfer coil 30 shown inFIG. 11, leakage power in the near field can also be suppressed. Inparticular, the power transfer coil 30 is formed so as to be symmetricalwhen viewed from one end of the outer coil 32 a connected to theterminal T31 and one end of the outer coil 32 b connected to theterminal T32, so that the effect of suppressing leakage magnetic fieldin the near field is enhanced. In addition, the equivalent circuit ofthe power transfer coil 30 is also formed so as to be symmetrical, sothat the effect of suppressing leakage magnetic field in the near fieldis further enhanced.

In addition, at the time of wireless power transfer using the powertransfer coil 30, power can be efficiently transmitted even if thepositions of the power transfer coils 30 at the power supplying end andpower receiving end are slightly misaligned from each other, asdescribed below.

FIG. 13 is a drawing describing the magnetic field generated by thepower transfer coil 30. FIG. 13 shows the power transfer coil 30 of FIG.11 in a simplified manner. In FIG. 13, components that are the same asthose shown in FIG. 11 are denoted by the same reference signs.

As shown in FIG. 13, in a case where current I is fed from the terminalT32, a magnetic flux generated by the inner coil 31 and a magnetic fluxgenerated by the outer coils 32 a and 32 b cause a magnetic flux as in amagnetic flux B31 shown in FIG. 13 extending from the back side of thedrawing plane toward the front side of the drawing plane to be generatedinside the inner coil 31.

The magnetic flux generated by the inner coil 31 and the magnetic fluxgenerated by the outer coils 32 a and 32 b cause the magnetic fluxbetween the inner coil 31 and the outer coils 32 a and 32 b to be “0”.Namely, a flux-free (including substantially flux-free; the same appliesto the term hereinafter) region is formed between the inner coil 31 andthe outer coils 32 a and 32 b.

Further, the magnetic flux generated by the inner coil 31 and themagnetic flux generated by the outer coils 32 a and 32 b cause amagnetic flux as in magnetic fluxes B32 a and B32 b shown in FIG. 13extending from the front side of the drawing plane toward the back sideof the drawing plane to be generated inside each of the outer coils 32 aand 32 b.

The magnetic flux generated by the inner coil 31 and the magnetic fluxgenerated by the outer coils 32 a and 32 b cause the magnetic fluxoutside the outer coils 32 a and 32 b to be “0”. Namely, the powertransfer coil 30 suppresses leakage magnetic field in its near field aswell.

FIG. 14 is a drawing describing power transmission efficiency. FIG. 14shows the power transfer coil 30 of FIG. 13. In addition, FIG. 14 showsthe power transfer coil P (power transfer coils Pa and Pb of the samesize) of FIG. 6 in a simplified manner.

In FIG. 14, the power transfer coil 30 configured to transmit power is apower transfer coil at the power supplying end, and the power transfercoils Pa and Pb configured to receive the power are power transfer coilsat the power receiving end. Hereinafter, when there is no need todistinguish between the power transfer coils Pa and Pb, the coils willbe collectively referred to as the power transfer coil P. The powertransfer coil P is larger than the inner coil 31 but is smaller than thecircular shape formed by two outer coils 32 a and 32 b.

As described with reference to FIG. 13, the flux-free region is formedbetween the inner coil 31 and the outer coils 32 a and 32 b. For thisreason, as can be seen from the power transfer coil Pa denoted by adotted line, even if a center of the power transfer coil Pa is slightlymisaligned from a center of the power transfer coil 30, the magneticflux B31 enters the power transfer coil Pa while the magnetic fluxes B32a and B32 b opposite in phase to the magnetic flux B31 do not enter thepower transfer coil Pa. Thus, in the power transfer coil 30, a decreasein power transmission efficiency can be suppressed even if the positionis slightly misaligned from the power transfer coil Pa at the powerreceiving end. Accordingly, if a center of the power transfer coil Pb islargely misaligned from the center of the power transfer coil 30 as canbe seen from the power transfer coil Pb denoted by a dot-and-dash line,the magnetic flux B31 and the magnetic fluxes B32 a and B32 b oppositein phase to the magnetic flux B31 would enter the power transfer coilPb, causing a decrease in power transmission efficiency.

The above has described a case where the power transfer coil at thepower receiving end is the circular power transfer coil P simply woundin one direction. However, the same can be applied in a case where thepower transfer coil at the power receiving end is the power transfercoil 30. Namely, in a case where the power transfer coils at the powersupplying end and power receiving end are each a power transfer coil 30,a decrease in power transmission efficiency can be suppressed even ifthe positions are slightly misaligned.

FIG. 15 is a graph showing a relation between a distance from a powertransfer coil and a magnitude of leakage magnetic field. The horizontalaxis of FIG. 15 represents the distance from the outer coil of the powertransfer coil, and the vertical axis thereof represents the magnitude ofleakage magnetic field. Measurements of leakage magnetic field wereperformed under conditions in which the power transfer coil at the powersupplying end and the power transfer coil at the power receiving endwere centered and were separated at a distance of 10 mm. Note that themagnitude of leakage magnetic field is relatively indicated by the valueof the power received by a non-resonant pickup coil.

A waveform W1 indicates the magnitude of leakage magnetic field of thepower transfer coil P shown in FIG. 6. The radius of the power transfercoil P is set to “2.5 cm”, and the number of turns thereof is set to“5”.

A waveform W2 indicates the magnitude of leakage magnetic field of thepower transfer coil 10 shown in FIG. 2. The radius of the inner coil 11is set to “2.5 cm”, and the number of turns thereof is set to “10”. Inaddition, the radius of the outer coils 12 a and 12 b is set to “3.5cm”, and the number of turns of each of the coils is set to “2.5”.

A waveform W3 indicates the magnitude of leakage magnetic field of thepower transfer coil 30 shown in FIG. 11. The radius of the inner coil 31is set to “2.5 cm”, and the number of turns thereof is set to “5”. Inaddition, the radius at an outer periphery of the outer coils 32 a and32 b is set to “4.5 cm”, the radius at an inner periphery thereof is setto “3.7 cm”, and the number of turns of each of the coils is set to “5”.

As indicated by the waveforms W2 and W3, it can be understood that thepower transfer coils 10 and 30 suppress leakage magnetic field ascompared to the power transfer coil P of FIG. 6 not having a structurefor cancelling magnetic flux. For example, it can be understood that thepower transfer coil 10 can obtain an effect of suppressing leakagemagnetic field of approximately 20 dB as compared to the power transfercoil P.

The power transfer coil 10 of FIG. 2 has the inner coil 11 connectedbetween two outer coils 12 a and 12 b, whereas the power transfer coil20 of FIG. 8 has the outer coil 22 connected between two inner coils 21a and 21 b. Therefore, the power transfer coil 20 can obtain measurementresults of leakage magnetic field similar to that of the waveform W2.For example, by setting the radius of the inner coils 21 a and 21 b ofthe power transfer coil 20 to “2.5 cm” and the number of turns of eachof the coils to “5”, and setting the radius of the outer coil 22 to “3.5cm” and the number of turns thereof to “5”, the magnitude of leakagemagnetic field indicated by the waveform W2 can be obtained.

FIG. 16 is a graph showing a relation between misalignment of the powertransfer coils and transmission properties. The horizontal axis of FIG.16 represents misalignment between the center of the power transfer coilat the power supplying end and the center of the power transfer coil atthe power receiving end. The vertical axis of FIG. 16 represents powertransmission properties (S21).

A waveform W11 indicates transmission properties of the power transfercoil P shown in FIG. 6. A waveform W12 indicates transmission propertiesof the power transfer coil 10 shown in FIG. 2. A waveform W13 indicatestransmission properties of the power transfer coil 30 shown in FIG. 11.The size and number of turns of each of the power transfer coils P, 10and 30 are the same as those described with reference to FIG. 15.

As indicated by the waveform W12, it is considered that the powertransfer coil 10 of FIG. 2 allows misalignment of up to approximately“10 mm”. As indicated by the waveform W13, it is considered that thepower transfer coil 30 of FIG. 11 allows misalignment of up to “17 mm”.Note that the power transfer coil 20 of FIG. 8 can obtain measurementresults of power transmission properties similar to that of the waveformW12.

As described above, the power transfer coil 30 includes: the outer coil32 a forming a loop outside the inner coil 31 such that a magnetic fluxopposite in phase to the magnetic flux outside the inner coil 31 isgenerated outside this loop, the outer coil 32 a having one endconnected to the terminal T31 and the other end connected to one end ofthe inner coil 31; and the outer coil 32 b forming a loop outside theinner coil 31 such that a magnetic flux opposite in phase to themagnetic flux outside the inner coil 31 is generated outside this loop,the outer coil 32 b having one end connected to the terminal T32 and theother end connected to the other end of the inner coil 31. Thus, thepower transfer coil 30 can suppress leakage magnetic field in the farfield and near field. In addition, a decrease in power transmissionefficiency can be suppressed even if misalignment between the coils atthe power supplying end and power receiving end occurs.

In addition, the inner coil 31 and the outer coils 32 a and 32 b of thepower transfer coil 30 are each formed so as to be symmetrical whenviewed from one end of the outer coil 32 a and one end of the outer coil32 b. Further, the equivalent circuit of the power transfer coil 30 isalso formed so as to be symmetrical when viewed from one end of theouter coil 32 a and one end of the outer coil 32 b. Thus, the powertransfer coil 30 can suppress leakage magnetic field in the near field.

In addition, a substantially same current is flowed in each of the innercoil 31 and outer coils 32 a and 32 b of the power transfer coil 30.Further, an area of the inner coil 31 is substantially equal to the sumof the areas of the outer coils 32 a and 32 b. Thus, the power transfercoil 30 can suppress leakage magnetic field in the near field.

In addition, the power transfer coil 30 includes the capacitor element33 a connected between the inner coil 31 and the outer coil 32 a, andthe capacitor element 33 b connected between the inner coil 31 and theouter coil 32 b. Thus, the power transfer coil 30 can suppress adecrease in the self-resonant frequency.

In addition, the power transfer coil 30 has the inner coil 31 and outercoils 32 a and 32 b formed on the same planar surface, so thatminiaturization can be achieved.

Fourth Embodiment

In the third embodiment, two outer coils 32 a and 32 b surrounding theinner coil 31 are arranged at separate positions. In a fourthembodiment, two inner coils are also arranged at separate positions.

FIG. 17 is a drawing showing a configuration example of a power transfercoil 40 according to the fourth embodiment. As shown in FIG. 17, thepower transfer coil 40 includes terminals T41 and T42, inner coils 41 aand 41 b, outer coils 42 a and 42 b, capacitor elements 43 a and 43 b,and a shaft 44. The inner coils 41 a and 41 b and the outer coils 42 aand 42 b are formed on the same planar surface. The power transfer coil40 is applied to a power supplying device (such as the charger 2 ofFIG. 1) configured to transmit power or a power receiving device (suchas the mobile device 3 of FIG. 1) configured to receive the power.

FIG. 17 shows a cross section of the shaft 44 extending in aperpendicular direction of the drawing plane. The shaft 44 rotates inthe clockwise or counterclockwise direction of FIG. 17.

The inner coils 41 a and 41 b have the same shape and are arranged atseparate positions. The inner coils 41 a and 41 b each have a crescentshape extending along a circular shape of the shaft 44 and collectivelyform a circular shape. The inner coil 41 a surrounds half of the shaft44 such that the shaft 44 is not inside the loop (is outside the loop)of the inner coil 41 a. The inner coil 41 b surrounds the remaining halfof the shaft 44 such that the shaft 44 is not inside the loop of theinner coil 41 b.

The outer coils 42 a and 42 b have the same shape and are arranged atseparate positions. The outer coils 42 a and 42 b each have a crescentshape extending along a circular shape of the inner coils 41 a and 41 band collectively form a circular shape. The outer coil 42 a surroundsthe inner coil 41 a, and the outer coil 42 b surrounds the inner coil 41b.

The outer coil 42 a forms a loop outside the inner coil 41 a and isformed such that a magnetic flux opposite in phase to a magnetic fluxoutside the inner coil 41 a is generated outside this loop. For example,the outer coil 42 a is formed such that a current is flowed in adirection opposite to a current flowing in the inner coil 41 a. Morespecifically, in a case where the current is flowing in the inner coil41 a in the counterclockwise direction, the outer coil 42 a is formedsuch that the current is flowed in the clockwise direction.

The outer coil 42 b forms a loop outside the inner coil 41 b and isformed such that a magnetic flux opposite in phase to a magnetic fluxoutside the inner coil 41 b is generated outside this loop. For example,the outer coil 42 b is formed such that a current is flowed in adirection opposite to a current flowing in the inner coil 41 b. Morespecifically, in a case where the current is flowing in the inner coil41 b in the counterclockwise direction, the outer coil 42 b is formedsuch that the current is flowed in the clockwise direction.

One end of the inner coil 41 a is connected to one end of the inner coil41 b. The other end of the inner coil 41 a is connected to the other endof the outer coil 42 a via the capacitor element 43 a. One end of theouter coil 42 a is connected to the terminal T41. The other end of theinner coil 41 b is connected to the outer coil 42 b via the capacitorelement 43 b. One end of the outer coil 42 b is connected to theterminal T42. In other words, two inner coils 41 a and 41 b arerespectively connected between two outer coils 42 a and 42 b via thecapacitor elements 43 a and 43 b. A combined capacitance of thecapacitor elements 43 a and 43 b is a value that resonates with acombined self-inductance of the inner coils 41 a and 41 b and outercoils 42 a and 42 b at the power transmitting frequency. A current forgenerating a magnetic field in the inner coils 41 a and 41 b and outercoils 42 a and 42 b is fed to the terminals T41 and T42.

The power transfer coil 40 is formed so as to be symmetrical when viewedfrom one end of the outer coil 42 a connected to the terminal T41 andone end of the outer coil 42 b connected to the terminal T42.

FIG. 18 is a drawing showing an equivalent circuit of the power transfercoil 40. FIG. 18 shows the terminals T41 and T42 of FIG. 17.

An inductor L41 of FIG. 18 corresponds to the outer coil 42 a of FIG.17. A capacitor element C41 of FIG. 18 corresponds to the capacitorelement 43 a of FIG. 17. An inductor L42 of FIG. 18 corresponds to theinner coil 41 a of FIG. 17. An inductor L43 of FIG. 18 corresponds tothe inner coil 41 b of FIG. 17. A capacitor element C42 of FIG. 18corresponds to the capacitor element 43 b of FIG. 17. An inductor L43 ofFIG. 18 corresponds to the outer coil 42 b of FIG. 17.

As shown in FIG. 18, the equivalent circuit of the power transfer coil40 is also formed so as to be symmetrical when viewed from one end ofthe outer coil 42 a connected to the terminal T41 and one end of theouter coil 42 b connected to the terminal T42.

The relation between the sizes of the inner coils 41 a and 41 b andouter coils 42 a and 42 b and the relation between the numbers of turnsof the inner coils 41 a and 41 b and outer coils 42 a and 42 b areobtained from the equations (1) and (2). For example, the sum of theareas of the inner coils 41 a and 41 b is set to be equal to the sum ofthe areas of the outer coils 42 a and 42 b. In addition, the inner coils41 a and 41 b and the outer coils 42 a and 42 b are wound such that thesame current is flowed therein. For example, the coils are wound suchthat the numbers of turns of the inner coils 41 a and 41 b and outercoils 42 a and 42 b are equal to one another. Thus, leakage magneticfield in the far field of the power transfer coil 40 is suppressed.

By providing the configuration of the power transfer coil 40 shown inFIG. 17, leakage power in the near field can also be suppressed. Inparticular, the power transfer coil 40 is formed so as to be symmetricalwhen viewed from one end of the outer coil 42 a connected to theterminal T41 and one end of the outer coil 42 b connected to theterminal T42, so that the effect of suppressing leakage magnetic fieldin the near field is enhanced. In addition, the equivalent circuit ofthe power transfer coil 40 is also formed so as to be symmetrical, sothat the effect of suppressing leakage magnetic field in the near fieldis further enhanced.

FIG. 19 is a drawing describing the magnetic field generated by thepower transfer coil 40. FIG. 19 shows the power transfer coil 40 of FIG.17 in a simplified manner. In FIG. 19, components that are the same asthose shown in FIG. 17 are denoted by the same reference signs.

As shown in FIG. 19, in a case where current I is fed from the terminalT42, a magnetic flux generated by the inner coils 41 a and 41 b and amagnetic flux generated by the outer coils 42 a and 42 b cause amagnetic flux in a region that is outside the loops of the inner coils41 a and 41 b and is surrounded by the inner coils 41 a and 41 b (regionwhere the shaft 44 is present) to be “0”. Namely, a flux-free region isformed in the region where the shaft 44 is present. Thus, in a casewhere the shaft 44 is made of metal, an eddy current can be suppressedfrom flowing in a surface of the shaft 44.

The magnetic flux generated by the inner coils 41 a and 41 b and themagnetic flux generated by the outer coils 42 a and 42 b cause amagnetic flux as in magnetic fluxes B41 a and B41 b shown in FIG. 19extending from the back side of the drawing plane toward the front sideof the drawing plane to be respectively generated inside the inner coils41 a and 41 b.

The magnetic flux generated by the inner coils 41 a and 41 b and themagnetic flux generated by the outer coils 42 a and 42 b cause themagnetic flux between the inner coils 41 a and 41 b and the outer coils42 a and 42 b to be “0”. Namely, a flux-free region is formed betweenthe inner coils 41 a and 41 b and the outer coils 42 a and 42 b.

Further, the magnetic flux generated by the inner coils 41 a and 41 band the magnetic flux generated by the outer coils 42 a and 42 b cause amagnetic flux as in magnetic fluxes B42 a and B42 b shown in FIG. 19extending from the front side of the drawing plane toward the back sideof the drawing plane to be respectively generated inside the outer coils42 a and 42 b.

The magnetic flux generated by the inner coils 41 a and 41 b and themagnetic flux generated by the outer coils 42 a and 42 b cause themagnetic flux outside the outer coils 42 a and 42 b to be “0”. Namely,the power transfer coil 40 suppresses leakage magnetic field in its nearfield as well.

As described above, the power transfer coil 40 includes: the outer coil42 a forming a loop outside the inner coil 41 a so as to surround theinner coil 41 a such that a magnetic flux opposite in phase to themagnetic flux outside the inner coil 41 a is generated outside thisloop, the outer coil 42 a having one end connected to the terminal T41and the other end connected to the other end of the inner coil 41 a; andthe outer coil 42 b forming a loop outside the inner coil 41 b so as tosurround the inner coil 41 b such that a magnetic flux opposite in phaseto the magnetic flux outside the inner coil 41 b is generated outsidethis loop, the outer coil 42 b having one end connected to the terminalT42 and the other end connected to the other end of the inner coil 41 b.Thus, the power transfer coil 40 can suppress leakage magnetic field inthe near field. In addition, a decrease in power transmission efficiencycan be suppressed even if misalignment between the coils at the powersupplying end and the power receiving end occurs. Further, a decrease inpower transmission efficiency caused by an eddy current flowed in asurface of the metal can be suppressed even if metal is present insidethe inner coils 41 a and 41 b.

In addition, the inner coils 41 a and 41 b and the outer coils 42 a and42 b of the power transfer coil 40 are each formed so as to besymmetrical when viewed from one end of the outer coil 42 a and one endof the outer coil 42 b. Further, the equivalent circuit of the powertransfer coil 40 is also formed so as to be symmetrical when viewed fromone end of the outer coil 42 a and one end of the outer coil 42 b. Thus,the power transfer coil 40 can suppress leakage magnetic field in thenear field.

In addition, a substantially same current is flowed in each of the innercoils 41 a and 41 b and outer coils 42 a and 42 b of the power transfercoil 40. Further, the sum of the areas of the inner coil 41 a and 41 bis substantially equal to the sum of the areas of the outer coils 42 aand 42 b. Thus, the power transfer coil 40 can suppress leakage magneticfield in the near field.

In addition, the power transfer coil 40 includes the capacitor element43 a connected between the inner coil 41 a and the outer coil 42 a, andthe capacitor element 43 b connected between the inner coil 41 b and theouter coil 42 b. Thus, the power transfer coil 40 can suppress adecrease in the self-resonant frequency.

In addition, the power transfer coil 40 has the inner coils 41 a and 41b and outer coils 42 a and 42 b formed on the same planar surface, sothat miniaturization can be achieved.

The above-described power transfer coils 10 to 40 of the embodimentseach have a circular shape but are not limited to this shape. Forexample, the power transfer coils 10 to 40 may each have a quadrangularshape.

Fifth Embodiment

In a fifth embodiment, a power supplying device and a power receivingdevice utilizing the power transfer coil of the first to fourthembodiments will be described.

FIG. 20 is a drawing showing a block configuration example of a powersupplying device 50 and power receiving device 60 according to the fifthembodiment. As shown in FIG. 20, the power supplying device 50 includesa controller 51, a communication unit 52, a display 53, an input unit54, a power transfer coil 55, a magnetic body 56, a power source V1,capacitor elements C51, C52 and C53, common-mode filters CF1 and CF2, anoscillator S1, an amplifier Z1, and an inductor L51. The power receivingdevice 60 includes a power transfer coil 61, a magnetic body 62, arectifier circuit 63, a power source circuit 64, a battery 65, acontroller 66, a communication unit 67, a capacitor element C61, andinductors L61 and L62. The charger 2 shown in FIG. 1 includes the powersupplying device 50 shown in FIG. 20, and the mobile device 3 includesthe power receiving device 60.

The controller 51 controls the entire the power supplying device 50. Thecommunication unit 52 performs wireless communication with the powerreceiving device 60. The controller 51 detects whether the powerreceiving device 60 is placed on a power supplying base (charging base)via the communication unit 52. In addition, the controller 51 performsauthentication of whether the power receiving device 60 placed on thepower supplying base is a charging target device. Further, thecontroller 51 controls the transmitting amount of the power.

The display 53 displays predetermined information in response to thecontrols of the controller 51. The input unit 54 receives the user'soperation and sends the received operation information to the controller51.

The power source V1 is grounded at a high frequency via the capacitorelement C51. The power source V1 supplies power to the amplifier Z1 viathe common-mode filter CF1. The common-mode filter CF1 is connectedbetween the power source V1 and the amplifier Z1 and suppressesconductive noise (common-mode noise) entering from a power source line.

An oscillation signal sent from the oscillator S1 is fed to theamplifier Z1. The amplifier Z1 performs a switching operation inresponse to the oscillation signal and sends a power transmitting signal(the transmitting power). In addition, the amplifier Z1 changes themagnitude (amplification factor) of the transmitting power in responseto the control of the controller 51. The transmitting power is sent tothe power transfer coil 55 via a low-pass filter and the common-modefilter CF2, the low-pass filter being formed by the inductor L51 and thecapacitor elements C52 and C53.

The low-pass filter is connected between the amplifier Z1 and the powertransfer coil 55 and removes harmonic noise in the transmitting power.The common-mode filter CF2 is connected between the amplifier Z1 and thepower transfer coil 55 and suppresses conduction noise in thetransmitting power, so that conduction noise is suppressed from beingunnecessarily radiated from the power transfer coil 55.

The power transfer coil 55 is the power transfer coil 10 of FIG. 2, thepower transfer coil 20 of FIG. 8, the power transfer coil 30 of FIG. 11or the power transfer coil 40 of FIG. 17. The power transfer coil 55wirelessly transfers the transmitting power sent from the amplifier Z1to the power receiving device 60 by using inductive coupling. Themagnetic body 56 suppresses a decrease in power transmission efficiencycaused by a metal casing or the like of the power supplying device 50.In addition, the magnetic body 56 suppresses heat generation of themetal casing or the like of the power supplying device 50.

The power transfer coil 61 of the power receiving device 60 is the powertransfer coil 10 of FIG. 2, the power transfer coil 20 of FIG. 8, thepower transfer coil 30 of FIG. 11 or the power transfer coil 40 of FIG.17. The power transfer coil 61 receives the power transmitted from thepower supplying device 50 by using inductive coupling. The magnetic body62 is identical to the magnetic body 56, suppresses a decrease in powertransmission efficiency and heat generation and the like of the metalcasing or the like of the power supplying device 50.

It is preferable that a power transfer coil of the same type as thepower transfer coil 55 of the power supplying device 50 is utilized forthe power transfer coil 61. In addition, the power transfer coil P ofFIG. 6 may be utilized for the power transfer coil 61. In a case wherethe power transfer coil P is utilized for the power transfer coil 61, aresonant capacitor element is connected in series between the powertransfer coil 61 and the low-pass filter. Further, the power transfercoil 61 and the capacitor element are series-resonated at the powertransmitting frequency.

The capacitor element C61 and the inductors L61 and L62 form thelow-pass filter. The low-pass filter suppresses harmonic noise in thepower received by the power transfer coil 61. In addition, the low-passfilter suppresses harmonic noise sent from the rectifier circuit 63, sothat harmonic noise sent from the rectifier circuit 63 is suppressedfrom being re-radiated from the power transfer coil 61.

The rectifier circuit 63 rectifies the power received by the powertransfer coil 61 (or converts an alternating current to a directcurrent). The power source circuit 64 sends the rectified power to thebattery 65, the controller 66 and the communication unit 67.

The battery 65 charges the power sent from the rectifier circuit 63. Thecontroller 66 controls the entire power receiving device 60. Thecontroller 66 controls the power source circuit 64 such that the power(voltage) sent from the power source circuit 64 is a suitable voltage.In addition, the controller 66 sends a charging state, such as theamount of the power currently being received and whether charging iscompleted, to the power supplying device 50 via the communication unit67. The communication unit 67 performs wireless communication with thepower supplying device 50.

FIG. 21 is a flowchart showing an operation example of the controller 51of the power supplying device 50. The controller 51 starts the processof the flowchart of FIG. 21 when, for example, the power is turned ON.

First, the controller 51 controls the amplifier Z1 such that a low poweris transmitted from the power transfer coil 55 (step S1). Namely, thecontroller 51 transmits power in which the power receiving device 60 canoperate at the minimum.

Next, the controller 51 determines whether wireless communication withthe power receiving device 60 is possible via the communication unit 52(step S2). Namely, the controller 51 determines whether the powerreceiving device 60 is placed on the power supplying base via wirelesscommunication with the power receiving device 60.

In step S2, if the controller 51 determines that communication was notpossible (“No” of S2), the controller 51 returns to the process of stepS1.

In step S2, if the controller 51 determines that communication ispossible (“Yes” of S2), the controller 51 performs an authenticationprocess as to whether the power receiving device 60 placed on the powersupplying base is an appropriated device (step S3). Here, the controller51 authenticates the power receiving device 60 as an appropriate deviceand proceeds to the process of step S4.

The controller 51 then determines whether to transfer power to the powerreceiving device 60 placed on the power supplying base (step S4). Forexample, the controller 51 receives information on whether the powerreceiving device 60 is fully charged from the power receiving device 60via the communication unit 52 and determines whether to transfer power.

In step S4, if the controller 51 determines to not transfer power (“No”of S4), the controller 51 displays an alert on the display 53 (step S5).For example, the controller 51 displays that the power receiving device60 placed on the power supplying base is fully charged on the display.Then, the controller 51 finishes transferring power to the powerreceiving device 60 to end the process of the flowchart.

In step S4, if the controller 51 determines to transfer power (“Yes” ofS4), the controller 51 determines whether the power receiving device 60placed on the power supplying base is provided with a power transfercoil configured to reduce leakage magnetic field (step S6). For example,the controller 51 receives information of the power transfer coilprovided in the power receiving device 60 from the power receivingdevice 60 via the communication unit 52 and determines that the deviceis provided with a power transfer coil configured to reduce leakagemagnetic field based on this information. Alternatively, if thecontroller 51 does not receive information of the power transfer coilprovided in the power receiving device 60 from the power receivingdevice 60 via the communication unit 52, the controller 51 determinesthat the power receiving device 60 is not provided with a power transfercoil configured to reduce leakage magnetic field.

The power transfer coil configured to reduce leakage magnetic field isthe power transfer coil 10 of FIG. 2, the power transfer coil 20 of FIG.8, the power transfer coil 30 of FIG. 11 or the power transfer coil 40of FIG. 17. The power transfer coil not configured to reduce leakagemagnetic field is, for example, the power transfer coil P of FIG. 6.Alternatively, the power transfer coil not configured to reduce leakagemagnetic field is a power transfer coil of different shape than thepower transfer coil 55. Specifically, this applies to a case where thepower transfer coil 55 is the power transfer coil 10 and the powertransfer coil 61 is the power transfer coil 20.

In step S6, if the controller 51 determines that the power receivingdevice 60 placed on the power supplying base is provided with a powertransfer coil configured to reduce leakage magnetic field (“Yes” of S6),the controller 51 transmits power of normal size (step S7).

Then, the controller 51 determines whether charging of the powerreceiving device 60 is completed (step S8). For example, the controller51 receives charging information from the power receiving device 60 viathe communication unit 52 and determines whether charging of the powerreceiving device 60 is completed.

In step S8, if the controller 51 determines that charging of the powerreceiving device 60 is not completed (“No” of S8), the controller 51repeats the process of step S8. On the other hand, in step S8, if thecontroller 51 determines that charging of the power receiving device 60is completed (“Yes” of S8), the controller 51 ends the process of theflowchart.

In step S6, if the controller 51 determines that the power receivingdevice 60 placed on the power supplying base is not provided with apower transfer coil configured to reduce leakage magnetic field (“No” ofS6), the controller 51 receives information from the user via the inputunit 54 on whether to transmit normal power even if leakage magneticfield is large (step S9). When receiving information from the user onwhether to transmit normal power, the controller 51 displays a screen onthe display 53 confirming whether to transmit normal power even ifleakage magnetic field is large.

If the controller 51 receives information from the user via the inputunit 54 that normal power is to be transmitted (“Yes” of S9), thecontroller 51 proceeds to the process of step S7.

If the controller 51 receives information from the user via the inputunit 54 that normal power is not to be transmitted (“No” of S9), a powerlower than the normal power is transmitted to the power receiving device60 (step S10). Namely, the controller 51 reduces the transmitting power,so that leakage magnetic field is small. In other words, the powersupplying device 50 reduces adverse effects on peripheral electronicdevices and the like caused by leakage magnetic field.

Then, the controller 51 determines whether charging of the powerreceiving device 60 is completed (step S11). In step S11, if thecontroller 51 determines that charging of the power receiving device 60is not completed (“No” of S11), the controller 51 repeats the process ofstep S11. On the other hand, in step S11, if the controller 51determines that charging of the power receiving device 60 is completed(“Yes” of S11), the controller 51 ends the process of the flowchart.

Note that the process of step S9 may be omitted.

As described above, the power supplying device 50 includes the amplifierZ1, the common-mode filter CF1 connected between the power source V1 andthe amplifier Z1, and the common-mode filter CF2 connected between theamplifier Z1 and the power transfer coil 55. Thus, the power supplyingdevice 50 can suppress leakage magnetic field. In addition, the powersupplying device 50 can suppress conduction noise in the transmittingpower, so that conduction noise is suppressed from being unnecessarilyradiated from the power transfer coil 55.

The power receiving device 60 includes the rectifier circuit 63configured to rectify the power received by the power transfer coil 61,and the low-pass filter connected between the power transfer coil 61 andthe rectifier circuit 63. Thus, the power receiving device 60 cansuppress leakage magnetic field. In addition, the power receiving device60 suppresses harmonics of the received power generated in the rectifiercircuit 63 from being re-radiated from the power transfer coil 61.

Examples of the charger 2 and mobile device 3 have been described aboveas application examples of the power supplying device 50 and powerreceiving device 60. Hereinafter, other application examples of thepower supplying device 50 and power receiving device 60 will bedescribed.

FIG. 22 is a drawing showing a first application example of the powersupplying device 50 and power receiving device 60. FIG. 22 shows aportion of an automobile. The automobile includes a charger 71, a centerconsole 73, a smart key 74, a car radio 75, a vehicle navigation system76, and a dashboard 77. In addition, FIG. 22 shows a mobile device 72.

The charger 71 includes the power supplying device 50 shown in FIG. 20.The mobile device 72 includes the power receiving device 60 shown inFIG. 20. The mobile device 72 is, for example, a smartphone, a tabletcomputer, a mobile phone or the like. The mobile device 72 is operableby the battery 65 within the power receiving device 60. The battery 65of the mobile device 72 is charged when placed on the charger 71.

The charger 71 is provided in the center console 73. The center console73 is formed so as to have a concave shape that extends along a shape ofthe mobile device 72, and the charger 71 is provided at this position.Thus, the mobile device 72 can be charged by the charger 71 withoutfalling from the charger 71 even while the vehicle is in motion. Thecharger 71 may be provided with a magnet at a center portion of thepower transfer coil, so that the mobile device 3 is magneticallyattracted to the charger 71. In this case, the charger 71 may beprovided on the dashboard 77.

As described above, the power supplying device 50 and the powerreceiving device 60 can be applied to an automobile. The power supplyingdevice 50 and the power receiving device 60 suppress leakage magneticfield, so that interference, undesirable behavior, noise contaminationand the like on wireless devices such as the smart key 74, the car radio75, the vehicle navigation system 76 and the like can be suppressed.

FIG. 23 is a drawing showing a second application example of the powersupplying device 50 and power receiving device 60. FIG. 22 shows alanding pad 81 and an unmanned aerial vehicle 82.

The landing pad 81 includes the power supplying device 50 shown in FIG.20. The unmanned aerial vehicle 82 includes the power receiving device60 shown in FIG. 20. Flight operation of the unmanned aerial vehicle 82is wirelessly controlled. The unmanned aerial vehicle 82 is capable offlying by the battery 65 within the power receiving device 60.

The unmanned aerial vehicle 82 lands on the landing pad 81. The unmannedaerial vehicle 82 is configured such that the power transfer coil 55within the landing pad 81 faces the power transfer coil 61 within theunmanned aerial vehicle 82 when the unmanned aerial vehicle 82 haslanded on the landing pad 81. In this manner, the battery 65 of theunmanned aerial vehicle 82 can be charged when the unmanned aerialvehicle 82 has landed on the landing pad 81.

As described above, the power supplying device 50 and the powerreceiving device 60 can be respectively applied to the landing pad 81and the unmanned aerial vehicle 82. The power supplying device 50 andthe power receiving device 60 suppress leakage magnetic field, so thatinterference, undesirable behavior, noise contamination or the like on acommunication circuit, GPS (Global Positioning System) or the likewithin the unmanned aerial vehicle 82 can be suppressed.

FIG. 24 is a drawing showing a third application example of the powersupplying device 50 and power receiving device 60. FIG. 24 shows acharger 91 and an automobile 92.

The charger 91 includes the power supplying device 50 shown in FIG. 20.The charger 91 is provided, for example, underground of a parking space.

The automobile 92 includes the power receiving device 60 shown in FIG.20. The automobile 92 is movable by the battery 65 within the powerreceiving device 60. In addition, each electronic device of theautomobile 92 is operable by the battery 65.

The automobile 92 is configured such that the power transfer coil 61faces the power transfer coil 55 of the charger 91 when the automobile92 has stopped at, for example, a predetermined location such as aparking space. In this manner, the battery 65 of the automobile 92 canbe charged.

As described above, the power supplying device 50 and the powerreceiving device 60 can be respectively applied to the charger 91 andthe automobile 92. The power supplying device 50 and the power receivingdevice 60 suppress leakage magnetic field, so that interference,undesirable behavior, noise contamination or the like on electronicdevices of the automobile 92 such as the smart key, an anti-theft deviceor an air pressure sensor can be suppressed.

FIG. 25 is a drawing showing a fourth application example of the powersupplying device 50 and power receiving device 60. FIG. 25 shows a stairelevator to be used by care receivers and the like having difficultiesin walking up or down a staircase. FIG. 25 shows a charger 101, a chair102, a rail 103 and a staircase 104.

The charger 101 includes the power supplying device 50 shown in FIG. 20.The charger 101 is provided on, for example, a wall located at an end ofthe rail 103.

The chair 102 includes the power receiving device 60 shown in FIG. 20.The chair 102 is connected to the rail 103 so as to be movable along therail 103. The rail 103 is attached to, for example, a wall so as toextend along the staircase 104. The chair 102 comprises a driving devicesuch as a motor and is movable along the rail 103 by the battery 65within the power receiving device 60.

The chair 102 is configured such that the power transfer coil 61 facesthe power transfer coil 55 of the charger 101 when the chair 102 hasmoved along the rail 103 and has arrived at a position of the charger101. In this manner, the battery 65 of the chair 102 can be charged.

As described above, the power supplying device 50 and the powerreceiving device 60 can be respectively applied to the charger 101 andthe chair 102 ascending and descending along the staircase 104. Thepower supplying device 50 and the power receiving device 60 suppressleakage magnetic field, so that adverse effects such as interference onmedical devices including a cardiac pacemaker or hearing aid worn by,for example, the care receiver can be suppressed.

FIG. 26 is a drawing showing a fifth application example of the powersupplying device 50 and power receiving device 60. FIG. 26 shows a liftto be used by a care receiver having difficulties in walking out from abed. FIG. 26 shows a charger 111, an electric lift 112, a sling sheet113, support columns 114 a and 114 b, a rail 115, and a bed 116.

The charger 111 includes the power supplying device 50 shown in FIG. 20.The charger 111 is attached to an end portion of the rail 115 supportedby the support columns 114 a and 114 b.

The electric lift 112 includes the power receiving device 60 shown inFIG. 20. The electric lift 112 is connected to the rail 115 so as to bemovable along the rail 115. The electric lift 112 comprises a drivingdevice such as a motor and is movable along the rail 115 by the battery65 within the power receiving device 60. The sling sheet 113 is attachedto the electric lift 112.

The electric lift 112 is configured such that the power transfer coil 61faces the power transfer coil 55 of the charger 111 when the electriclift 112 has moved along the rail 115 and has arrived at a position ofthe charger 111. In this manner, the battery 65 of the electric lift 112can be charged.

As described above, the power supplying device 50 and the powerreceiving device 60 can be respectively applied to the charger 111 andthe electric lift 112. The power supplying device 50 and the powerreceiving device 60 suppress leakage magnetic field, so that adverseeffects such as interference on medical devices including the cardiacpacemaker or hearing aid worn by, for example, the care receiver can besuppressed.

In the foregoing, the present invention has been described based on theembodiments. However, each of the embodiments has been classifiedaccording to its main processing content in order to facilitateunderstanding of configurations of the power transfer coil, powersupplying device and power receiving device. The invention of thepresent application is not to be limited by the manner into which eachcomponent is classified or by the name of the component. Configurationsof the power transfer coil, power supplying device and power receivingdevice can be further classified into several components according tothe processing contents. In addition, a single component can beclassified so as to perform several processes. Further, the process ofeach component may be performed by a single hardware device or may beperformed by a plurality of hardware devices.

In addition, each of the processes in the above-described flowchart hasbeen divided according to its main processing content in order tofacilitate understanding of processes of the power supplying device andpower receiving device. The invention of the present application is notto be limited by the manner to which the process is divided or by thename of the process. Processes of the power supplying device and powerreceiving device can be further divided into several process accordingto the processing content. In addition, a single process can be dividedso as to include several processes.

In addition, a technical scope of the present invention is not to belimited to the description of the foregoing embodiments. It should beapparent to one skilled in the art that various modifications andimprovements can be added to the foregoing embodiments. It should alsobe obvious from the disclosure of the scope of the claims thatembodiments to which such modifications or improvements are added can beincluded in the technical scope of the present invention. In addition,each of the embodiments can be combined with one another.

In addition, the position, size, shape, range or the like of eachconfiguration shown in the drawings and the like may not represent theactual position, size, shape, range or the like in order to facilitateunderstanding of the present invention. Thus, the present invention isnot necessarily limited to the position, size, shape, range or the likedisclosed in the drawings and the like.

(Additional Statement 1)

A power transfer coil comprising:

a first inner coil;

a second inner coil having one end connected to one end of the firstinner coil;

a first outer coil forming a first loop outside the first inner coil soas to surround the first inner coil such that a magnetic flux oppositein phase to a magnetic flux outside the first inner coil is generatedoutside the first loop, the first outer coil having one end connected toa first terminal and the other end connected to the other end of thefirst inner coil; and

a second outer coil forming a second loop outside the second inner coilso as to surround the second inner coil such that a magnetic fluxopposite in phase to a magnetic flux outside the second inner coil isgenerated outside the second loop, the second outer coil having one endconnected to a second terminal and the other end connected to the otherend of the second inner coil.

(Additional Statement 2)

A power supplying device comprising:

an amplifier;

a first common-mode filter connected between a power source and theamplifier;

a power transfer coil that includes: an inner coil; a first outer coilformed so as to surround the inner coil such that a magnetic fluxopposite in phase to a magnetic flux outside the inner coil is generatedoutside the first outer coil, the first outer coil having one endconnected to a first terminal and the other end connected to one end ofthe inner coil; and a second outer coil formed so as to surround theinner coil such that a magnetic flux opposite in phase to the magneticflux outside the inner coil is generated outside the second outer coil,the second outer coil having one end connected to a second terminal andthe other end connected to the other end of the inner coil; and

a second common-mode filter connected between the amplifier and thepower transfer coil.

(Additional Statement 3)

A power receiving device comprising:

a power transfer coil that includes: an inner coil; a first outer coilformed so as to surround the inner coil such that a magnetic fluxopposite in phase to a magnetic flux outside the inner coil is generatedoutside the first outer coil, the first outer coil having one endconnected to a first terminal and the other end connected to one end ofthe inner coil; and a second outer coil formed so as to surround theinner coil such that a magnetic flux opposite in phase to the magneticflux outside the inner coil is generated outside the second outer coil,the second outer coil having one end connected to a second terminal andthe other end connected to the other end of the inner coil;

a rectifier circuit configured to rectify power received by the powertransfer coil; and

a low-pass filter connected between the power transfer coil and therectifier circuit.

LIST OF REFERENCE SIGNS

1: wireless power transfer system

2: charger

3: mobile device

10, 10 a, 10 b: power transfer coil

11: inner coil,

12 a, 12 b: outer coil

13 a, 13 b: capacitor element

T11, T12: terminal

21 a, 21 b: inner coil

22: outer coil,

23 a, 23 b: capacitor element

T21, T22: terminal

31: inner coil

32 a, 32 b: outer coil

33 a, 33 b: capacitor element

T31, T32: terminal

41 a, 41 b: inner coil

42: outer coil

43 a, 43 b: capacitor element

44: shaft

T41, T42: terminal

50: power supplying device

60: power receiving device

1. A power transfer coil comprising: an inner coil; a first outer coilformed so as to surround the inner coil such that a magnetic fluxopposite in phase to a magnetic flux outside the inner coil is generatedoutside the first outer coil, the first outer coil having one endconnected to a first terminal and the other end connected to one end ofthe inner coil; and a second coil formed so as to surround the innercoil such that a magnetic flux opposite in phase to the magnetic fluxoutside the inner coil is generated outside the second coil, the secondcoil having one end connected to a second terminal and the other endconnected to the other end of the inner coil.
 2. The power transfer coilaccording to claim 1, wherein the first outer coil and the second outercoil have a substantially same shape and are arranged at a substantiallysame position.
 3. The power transfer coil according to claim 1, whereinthe inner coil, the first outer coil and the second outer coil are eachformed so as to be symmetrical when viewed from one end of the firstouter coil and one end of the second outer coil.
 4. The power transfercoil according to claim 1, wherein a current approximately twice aslarge as a sum of a current flowing in the first outer coil and acurrent flowing in the second outer coil is flowed in the inner coil,and a radius of the first outer coil and second outer coil isapproximately 2^(1/2) times as large as a radius of the inner coil. 5.The power transfer coil according to claim 1, further comprising: afirst capacitor element connected between the inner coil and the firstouter coil; and a second capacitor element connected between the innercoil and the second outer coil.
 6. A power transfer coil comprising: afirst inner coil having one end connected to a first terminal; a secondinner coil having one end connected to a second terminal; and an outercoil formed so as to surround the first inner coil and the second innercoil such that a magnetic flux opposite in phase to a magnetic fluxoutside the first inner coil and the second inner coil is generatedoutside the outer coil, the outer coil having one end connected to theother end of the first inner coil and the other end connected to theother end of the second inner coil.
 7. The power transfer coil accordingto claim 6, wherein the first inner coil and the second inner coil havea substantially same shape and are arranged at a substantially sameposition.
 8. The power transfer coil according to claim 6, wherein thefirst inner coil, the second inner coil and the outer coil are eachformed so as to be symmetrical when viewed from one end of the firstinner coil and one end of the second inner coil.
 9. The power transfercoil according to claim 6, wherein a current approximately twice aslarge as a current flowing in the outer coil is flowed in the firstinner coil and the second inner coil, and a radius of the outer coil isapproximately 2^(1/2) times as large as a radius of the first inner coiland second inner coil.
 10. The power transfer coil according to claim 6,further comprising: a first capacitor element connected between thefirst inner coil and the outer coil; and a second capacitor elementconnected between the second inner coil and the outer coil.
 11. A powertransfer coil comprising: an inner coil; a first outer coil forming afirst loop outside the inner coil such that a magnetic flux opposite inphase to a magnetic flux outside the inner coil is generated outside thefirst loop, the first outer coil having one end connected to a firstterminal and the other end connected to one end of the inner coil; and asecond outer coil forming a second loop outside the inner coil such thata magnetic flux opposite in phase to the magnetic flux outside the innercoil is generated outside the second loop, the second outer coil havingone end connected to a second terminal and the other end connected tothe other end of the inner coil.
 12. The power transfer coil accordingto claim 11, wherein the first loop and the second loop have asubstantially same size and are arranged at separate positions.
 13. Thepower transfer coil according to claim 11, wherein the inner coil, thefirst outer coil and the second outer coil are each formed so as to besymmetrical when viewed from one end of the first outer coil and one endof the second outer coil.
 14. The power transfer coil according to claim11, wherein a substantially same current is flowed in each of the innercoil, first outer coil and second outer coil, and an area of the innercoil is substantially equal to a sum of an area of the first outer coiland an area of the second outer coil.
 15. The power transfer coilaccording to claim 11, further comprising: a first capacitor elementconnected between the inner coil and the first outer coil; and a secondcapacitor element connected between the inner coil and the second outercoil.